Hydraulic dual-circuit brake system

Abstract

A hydraulic dual-circuit brake system, with an anti-skid system (ABS) and traction control (ASR) for motor vehicles having a four-channel hydraulic unit with control valves, a return pump with two separate pump elements for each brake circuit, and two low-pressure reservoirs connected to the inlets of the pump elements. For supplying brake pressure in the traction control mode, at least one brake fluid reservoir is provided, which communicates with a pump element assigned to a brake circuit having at least one driven wheel, and a reversing valve is disposed in each connecting line between the master brake cylinder and the outlet of such a pump element. For the sake of problem-free initiation of braking during the traction control mode without the danger of unstable driving conditions, the brake fluid reservoir is embodied as an active, controllable reservoir, and the reversing valve is embodied such that in its reversed position a check valve having a blocking direction toward the master brake cylinder is operative.

What is claimed and desired to be secured by Letters Patent of the United States is: 
     
       1. A hydraulic dual-circuit brake system with an anti-skid system and traction control for motor vehicles including driven and nondriven wheels, having a master brake cylinder with first and second brake circuit outlets (16, 17) for controlling a brake pressure by brake pedal actuation; a four-channel hydraulic unit with first, second, third and fourth outlet channels (21, 22, 23, 24), said first and second outlet channels are distributed to first and second brake circuits connected to said first brake circuit outlet and said third and fourth outlet channels are distributed to third and fourth brake circuits connected to said second brake circuit outlet for connection with first, second, third, and fourth wheel brake cylinders (11, 12, 13, 14) of the driven and nondriven wheels, first, second, third, and fourth electromagnetic input control valves (31, 32, 33, 34) having an inlet connected respectively with said first, second, third and fourth brake circuits and an outlet connected to said first, second, third and fourth outlet circuits respectively for controlling a brake pressure dependent on wheel slip in the wheel brake cylinders, each of said first, second, third, and fourth electromagnetic input control valves (31, 32, 33, 34) include an output connected respectively with said first, second, third and fourth outlet channels (21, 22, 23, 24) and each of said first and second electromagnetic input control valves include an inlet connected to a first connecting line (36) connected to said first brake circuit outlet and each of said third and fourth electromagnetic input control valves include an inlet connected to a second connecting line (37) connected with said second brake circuit outlet of the master brake cylinder, a first reversing valve (38") disposed in said second brake circuit between said first brake circuit outlet of the master brake cylinder and the inlet of said second electromagnetic input control valve assigned to said second brake circuit which is assigned to a first driven wheel; a second reversing valve (39") disposed in said third brake circuit between said second brake circuit outlet of the master brake cylinder and the inlet of said third electromagnetic input control valve assigned to said third brake circuit which is assigned to a second driven wheel, each of said reversing valves is triggered during a traction control operation, a precharging pump (69) having an inlet connected to a brake fluid reservoir (71) and an output connected with an input reservoir of first and second combination reservoirs (56', 57'), a return pump (27) including first and second pump elements (28, 29), said first and second pump elements each include an inlet connected with an outlet reservoir of each of said first and second combination reservoirs, said first pump element having an outlet connected with a first damping chamber (45) and to said second brake circuit between said first reversing valve (38") and said second electromagnetic control valve (31), said second pump element having an outlet connected with a second damping chamber (46) and to said third brake circuit between said second reversing valve (39") and said third electromagnetic control valve (33), said first combination reservoir having a first outlet connected with a connection to each of said first and second electromagnetic control valves and to a connection of said first reversing valve (38"), said second combination reservoir having a second outlet connected with a connection to each of said third and fourth electromagnetic control valves (33, 34) and to a connection with said second reversing valve, during traction control of one of the driven wheels either the first or second reversing valve disconnects the master brake cylinder to the brake circuit so that the driven wheels are controlled by the reversing valve, and the first and fourth electromagnetic control valves communicate directly with the master brake cylinder. 
     
     
       2. A hydraulic dual-circuit brake system as claimed in claim 1 which includes a bypass line (72) from the output of the precharging pump to the reservoir (71), a bypass control valve (73) in said bypass line, said bypass control valve blocks fluid flow back to the reservoir (71) during traction control and opens said bypass control valve subsequent to traction control. 
     
     
       3. A hydraulic dual circuit brake system as claimed in claim 1 in which each of said first and second combination reservoirs include a reservoir cylinder (67) having a closed end and an open end, a chamber in said cylinder, an end plate (76) which closes said open end to form a piston (66) in said chamber which divides the chamber into first and second reservoir chambers (74, 75), a first spring (50) in said reservoir chamber (74), a second spring (49) in said second chamber (75), said reservoir cylinder (67) includes a central connection opening (78) in said closed end of said reservoir cylinders which extends to said first reservoir, and a central connection bore in said end plate which extends to said second reservoir chamber. 
     
     
       4. A hydraulic dual circuit brake system as claimed in claim 2 in which each of said first and second combination reservoirs include a reservoir cylinder (67) having a closed end and an open end, a chamber in said cylinder, an end plate (76) which closes said open end to form a piston (66) in said chamber which divides the chamber into first and second reservoir chambers (74, 75), a first spring (50) in said reservoir chamber (74), a second spring (49) in said second chamber (75), said reservoir cylinder (67) includes a central connection opening (78) in said closed end of said reservoir cylinders which extends to said first reservoir, and a central connection bore in said end plate which extends to said second reservoir chamber.